In waveform display instruments, such as oscilloscopes, a popular user convenience feature is the use of cursors for making differential time and voltage measurements. Such cursors are typically in the form of horizontal or vertical lines, or even intensified dots, which may be positioned independently to points of interest along a waveform. One such system employing two intensified dots is taught in U.S. Pat. No. 3,881,133, which is assigned to the assignee of the present invention. Here a linear potentiometer with an associated calibrated readout dial permits one dot to be moved along a waveform with respect to the other dot while providing a readout of the time difference.
An extension of the two-dot time measurement system is the coupling of volts cursors in the form of horizontal lines to the time dots so that a voltage difference may be read out between the two times.
It would be desirable to provide a user-convenience feature in which the readout is an absolute ground-referenced voltage at a particular selectable time along the waveform.